Heat exchanger

ABSTRACT

The invention relates to a heat exchanger, particularly a radiator for a heating or air conditioning unit in motor vehicles, which cools a coolant. Said heat exchanger ( 1 ) is penetrated by air, comprises collector pipes (S 1,  S 2,  S 2,  S 4 ) and several essentially horizontally disposed pipes ( 5 ), and is divided into several partial blocks (T 1,  T 2,  T 3,  T 4 ). The surfaces of the inventive partial blocks are selected according to the dimensions of structural space-related zones having different air temperatures inside the assembly space of the heat exchanger, the partial block which is first penetrated by the coolant being arranged within a structural space-related zone having a higher air temperature, preferably within the zone having the highest air temperature.

The invention relates to a heat exchanger, in particular a radiator fora heating or air-conditioning system for motor vehicles, according tothe preamble of claim 1, 8, 9, 10 or 11.

EP 0 845 648 A2 discloses a flat-tube heat exchanger, in particular acondenser of the serpentine type, with a flat-tube block consisting ofone or more flat tubes which issue with preferably twisted end portionson the opposite or on the same tube block side into respectiveconnection-space components, that is to say header tubes, so that,should the header tubes be arranged on the same tube block side, twoheader tubes running adjacently and parallel to one another areprovided. In this case, a plurality of serpentine-shaped flat tubes maybe provided, in which adjacent flat tubes are arranged with theirinlet-side or their outlet-side tube portions adjacently to one anotherin the longitudinal direction of the header tubes, the serpentinescomprising a plurality of 180° bends. A corresponding arrangementprevents heat transmission losses, but still leaves much to be desired.

EP 0 414 433 discloses a duplex heat exchanger which allows a coolantthroughflow in cross countercurrent, in that two flat heat exchangersarranged one behind the other, designated hereafter as blocks, in eachcase with two header tubes which are connected to one another via amultiplicity of flat tubes, are provided. The two blocks are connectedto one another by means of flanges and O-ring seals, for which purposethey have to be constructed, tensioned and soldered separately and,after soldering, connected to one another. The supply of the coolant tothe block through which the flow passes first takes place in an upperregion, the outlet at the bottom, and, in the second block through whichthe flow subsequently passes, inlet can take place both at the bottomand at the top, and outlet takes place correspondingly at the top or atthe bottom. A duplex heat exchanger of this type which consists of twoblocks entails a multiplicity of individual parts and a relatively highoutlay in production terms, so that production is costly. Furthermore, aheat exchanger of this type still leaves much to be desired with regardto thermal properties.

Moreover, DE 100 43 439 A1 discloses a radiator for a supercriticalsteam compression refrigerating circuit, in which a coolant outlet isprovided in a higher position than a coolant inlet, with respect to avertical direction, such that coolant flows from an underside of theradiator to a top side, as a result of which an improvement in thecooling efficiency of the coolant is promised. Even a radiator of thistype, however, still leaves much to be desired in terms of coolantefficiency.

The object of the invention is to improve a heat exchanger of the typeinitially mentioned.

This object is achieved by means of a heat exchanger having the featuresof claim 1, 8, 9, 10 or 11. The dependent claims relate to advantageousrefinements and developments of the invention.

The main idea of the invention is to make the surfaces of the subblocksdependent on the size of installation-space-related zones havingdifferent air temperatures and to cause coolant to flow first throughthe subblock within an installation-space-related zone having a higherair temperature, the subblock being arranged preferably within the zonehaving the highest air temperature.

In an advantageous embodiment of the heat exchanger, the height of thesubblock through which coolant flows first is at least as great as theheight of the zone having an increased air temperature.

In a further advantageous embodiment of the heat exchanger, the numberof tubes arranged in the horizontal direction in a subblock is dependenton the installation-space-related air temperature zone within which thecorresponding subblock is arranged.

In a particularly advantageous embodiment of the invention, the numberof tubes of a subblock within a zone having a higher temperature islarger than the number of tubes of a subblock which is arranged within azone having a lower temperature, the ratio of the number of tubes of thesubblock within the zone having a higher temperature to the number oftubes of the subblock within the zone having a lower temperature beingselectable in the range of 1:1 to 3:1.

In a particularly advantageous embodiment of the invention, at least twosubblocks are arranged one behind the other and at least two subblocksare arranged one above the other, the coolant flowing through thesubblocks in succession, and the order of throughflow beingpredeterminable, as desired, by means of structural measures.

Preferably, the coolant flows through at least two of the subblocks incountercurrent to the airstream.

In a particularly advantageous embodiment, the heat exchanger issubdivided into four subblocks through which the flow passes insuccession, the subblocks through which the flow passes first beingarranged below the subblocks through which the flow subsequently passes,the first and the second subblock and also the third and the fourthsubblock being arranged in each case at the same height. Such a heatexchanger is suitable, in particular, for an installation space inwhich, as a consequence of installation space, there is in a lowerregion of the installation space a zone having a higher air temperaturethan in an upper region.

In an alternative version of the heat exchanger, the subblocks throughwhich the flow passes first are arranged above the subblocks throughwhich the flow subsequently passes, the first and the second subblockand also the third and the fourth subblock being arranged in each caseat the same height. This alternative version of the heat exchanger issuitable, in particular, for an installation space in which, as aconsequence of installation space, there is in an upper region of theinstallation space a zone having a higher air temperature than in alower region.

The temperature of the coolant in the various subblocks differs as afunction of the zones having different temperature. Thus, in anembodiment of the heat exchanger which is arranged in an installationspace in which there is in a lower region of the installation space azone having a higher air temperature than in an upper region, thetemperature of the coolant is higher in the lower subblocks than in theupper subblocks, the temperature of one or of both rear subblocks beinghigher than the temperature of the corresponding front subblock. In analternative embodiment of the heat exchanger which is arranged in aninstallation space in which there is in an upper region of theinstallation space a zone having a higher air temperature than in alower region, the temperature of the coolant is higher in the uppersubblocks than in the lower subblocks, the temperature of one or of bothrear subblocks being higher than the temperature of the correspondingfront subblock.

In all the instances mentioned, for example, R 134a and carbon dioxidemay be used as coolant. In particular, carbon dioxide in a supercriticalstate, that is to say when there is a pure gas flow in the heatexchanger, is suitable for a heat exchanger according to the invention.

Preferably, a throughflow of at least two of the four subblocks bycoolant takes place in cross countercurrent to the air. More effectiveheat transmission occurs as a result of cross countercurrent operation.

In particular, a diagonal deflection is provided between the secondsubblock and the third subblock, so that cross countercurrent operationtakes place in all the subblocks.

Preferably, the diagonal deflection is formed by means of a one-parttransition flange which is connected to two header tubes, to be preciseto the header tube assigned to the second subblock and to the headertube assigned to the third subblock.

Preferably, in the region of the diagonal deflection, a tube, inparticular a flat tube, is provided, through which coolant does not flowor flows to only a minimal extent, with the result that a decoupling ofheat transmission takes place.

Preferably, the tubes which connect the header tubes and in the regionof which heat transfer takes place are formed by flat tubes, the flattubes being twisted through 90° upstream and downstream of a 180°bending point in the vicinity of the header tubes and on that side ofthe heat exchanger which is located opposite the header tubes.

In a further embodiment, the subblocks are closed off on both sides bymeans of header tubes, in which case at least two subregions may also beclosed off on at least one side by means of a common header tube.

Preferably, the air flowing through the heat exchanger comes intocontact with two or more regions of different temperature, the maximumair temperature difference between air inlet and air outlet beingsmaller than one and a half times the temperature difference betweencoolant inlet and coolant outlet, the coolant used being carbon dioxidein the supercritical state. In this case, temperatures of around 150° C.prevail at the coolant inlet and of around 50° C. at the outlet.

Preferably, the tubes arranged essentially in the horizontal directionare thermally separated from one another, for example by means of an airgap.

Preferably, the individual subblocks, too, are thermally separated fromone another.

Preferably, the header tubes, too, are decoupled essentially thermally.There is thermal contact only at the diagonal deflection and, dependingon design, also at the connecting flanges.

Preferably, the cooling ribs arranged between the tubes are likewisedecoupled thermally. This is achieved, for example, by each subblockhaving its own cooling ribs.

The invention is explained in detail hereafter by means of an exemplaryembodiment, with reference to the drawing, in which:

FIG. 1 shows a front view of a flat-tube heat exchanger according to theexemplary embodiment;

FIG. 2 shows a section through the flat-tube heat exchanger of FIG. 1along the line II-II in FIG. 1;

FIG. 3 to 6 show a transition flange in various views; and

FIG. 7 to 9 show a connection piece in various views.

FIGS. 1 and 2 show a flat-tube heat exchanger for a heating orair-conditioning system of a motor vehicle, which serves as a radiator 1and is part of a coolant circuit, not illustrated, and which serves forcooling a coolant, in particular CO₂, with the aid of the air flowingthrough the radiator 1. FIG. 2 illustrates the airstream symbolically byan arrow pointing to the radiator 1 from the left. The CO₂ is normallyin a supercritical state as a pure gas flow, temperatures of around 150°C. prevailing at the inlet 2 into the radiator 1. A cooling of thecoolant takes place in the radiator 1, so that temperatures of around50° C. prevail at the outlet 3.

In order to allow an optimum utilization of the air flowing through theradiator 1, the radiator 1 is subdivided into 2×2 subblocks which aredesignated hereafter as T1, T2, T3 and T4. In this case, in theinstalled state, the subblocks T1 and T2 are arranged within a zone 4having a higher air temperature and below the subblocks T3 and T4. Theheight h of the two subblocks T1, T2 which are arranged within the zone4 having the higher air temperature is greater than the height H of thezone 4 having an increased air temperature, the value of the airtemperature in the zone 4 being higher than the air temperature in theremaining regions of the installation space of the radiator 1. A headertube S1, S2, S3, S4 is connected to each subblock, in each case twoheader tubes S1, S2 and S3, S4 being arranged at the correspondingheight of the subblocks T1, T2 and T3, T4. Between the header tubes S1,S2 and S3, S4 are arranged a plurality of flat tubes 5, through whichthe coolant can pass from one header tube Si or S3 to the adjacentheader tube S2 or S4, for which purpose the flat tubes 5 have a U-shapedrun. They are twisted in each case through 90° in a known way in thevicinity of the respective header tube S1, S2, S3, S4. Between the flattubes 5 are arranged ribs (not illustrated) which assist the heatexchange, and these ribs may be divided in two, that is to say thesubblocks T1, T2 and T3, T4 arranged one behind the other have in eachcase their own ribs. It is also possible, however, to decouple the ribsof the subblocks thermally by means of slots.

So that the coolant can flow through the radiator 1 in crosscountercurrent to the air, a diagonal reversal 6 from subblock T2 tosubblock T3 is provided, as is indicated in FIG. 2 by an arrow depictedinto the radiator 1. For this purpose, a transition flange 7, as isillustrated in FIG. 3 to 6, is provided between the two header tubes S2and S3, the zone of the flat tube 5′ lying at the boundary of the twosubblocks T2, T3 being utilized, in that the partitions of the twoheader tubes S2 and S3 are mounted so as to be offset by the amount ofone transverse division. The middle flat tube 5′ is thus“short-circuited” and has scarcely any flow passing through it, at themost as a result of a slight pressure difference which occurs betweenthe two header tubes S2 and S3 on account of the slight throttlingeffect in the transition flange 7. In this case, the flat tube 5′through which no flow or only a minimal flow passes has the secondaryeffect that thermal decoupling is achieved between the subblocks T1, T3and T2, T4. The transition flange 7 is conventionally produced, togetherwith the two partitions, as one component and is also soldered duringthe soldering of the radiator 1.

The header tubes S1 and S2 or S3 and S4 are connected to one another ineach case at the inlet 2 or at the outlet 3 via a connection piece 9, asis illustrated in FIG. 7 to 9, so that coolant can also pass directlyinto the header tube S2 or can flow directly out of the header tube S3.

For thermal decoupling, the collection of the coolant takes place, afterthe latter has flowed through the subblocks T1 and T2 or T3 and T4, inheader tubes S1, S3 and S2, S4 designed separately. The thermal couplingof the subblocks T1 and T2 or T3 and T4 via the one-part ribs may bereduced by the slotting of the rib or by any other suitable measure.

According to the exemplary embodiment illustrated, there is a divisionof the subblocks T1, T2 in relation to the subblocks T3, T4 of 50:50,but the division should preferably be made decreasingly, that is to say,for example, 60:40 or 70:30, since, as in the condenser, the outletdensity is higher and consequently the volume of flow lower than at theinlet. Moreover, the gas radiator likewise serves in a subcritical stateas a condenser.

List of Reference Symbols

-   1 Radiator-   2 Inlet-   3 Outlet-   4 Zone having a higher temperature-   5, 5′ Flat tube-   6 Diagonal reversal-   7 Transition flange-   9 Connection piece-   S, S2, S3, S4 Header tube-   T1, T2, T3, T4 Subblock-   H Height of the zone having a higher temperature-   h Subblock height

1. A heat exchanger, in particular radiator for a heating orair-conditioning system of motor vehicles for the cooling of coolant,which heat exchanger has air flowing through it, with header tubes (S1,S2, S3, S4) and with a plurality of tubes (5) arranged essentially inthe horizontal direction, the heat exchanger (1) being subdivided into aplurality of subblocks (T1, T2, T3, T4), characterized in that thesurfaces of the subblocks are dependent on the size ofinstallation-space-related zones having a different air temperature inthe installation space of the heat exchanger, the subblock through whichcoolant flows first being arranged within an installation-space-relatedzone having a higher air temperature, preferably within the zone havingthe highest air temperature.
 2. The heat exchanger as claimed in claim1, characterized in that the height of the subblock through whichcoolant flows first is at least as great as the height of the zonehaving an increased air temperature.
 3. The heat exchanger as claimed inclaim 1, characterized in that the number of tubes arranged in thehorizontal direction in a subblock is dependent on theinstallation-space-related air temperature zone within which thecorresponding subblock is arranged.
 4. The heat exchanger as claimed inclaim 3, characterized in that the number of tubes in the first subblockwhich is arranged within a zone having a higher temperature is largerthan the number of tubes of the second subblock which is arranged withina zone having a lower temperature.
 5. The heat exchanger as claimed inclaim 3, characterized in that the ratio of the number of tubes of thefirst subblock to the number of tubes of the second block is selectablein the range of 1:1 to 3:1.
 6. The heat exchanger as claimed in claim 1,characterized in that at least two subblocks are arranged one behind theother and at least two subblocks one above the other, the coolantflowing through the subblocks in succession, and the order ofthroughflow being predeterminable, as desired, by means of structuralmeasures.
 7. The heat exchanger as claimed in claim 6, characterized inthat the coolant flows through at least two of the subblocks incountercurrent to the airstream.
 8. A heat exchanger, in particularradiator for a heating or air-conditioning system of motor vehicles forthe cooling of coolant, which heat exchanger has air flowing through it,with header tubes (S1, S2, S3, S4) and with a plurality of tubes (5)arranged essentially in the horizontal direction, the heat exchanger (1)being subdivided into four subblocks (T1, T2, T3, T4), through which theflow passes in succession, characterized in that the subblocks (T1, T2)through which the flow passes first are arranged below the subblocks(T3, T4) through which the flow subsequently passes, the first and thesecond subblock (T1 and T2) and also the third and the fourth subblock(T3 and T4) being arranged in each case at the same height.
 9. A heatexchanger, in particular radiator for a heating or air-conditioningsystem of motor vehicles for the cooling of coolant, which heatexchanger has air flowing through it, with header tubes (S1, S2, S3, S4)and with a plurality of tubes (5) arranged essentially in the horizontaldirection, the heat exchanger (1) being subdivided into four subblocks(T1, T2, T3, T4) through which the flow passes in succession,characterized in that the subblocks (T3, T4) through which the flowpasses first are arranged above the subblocks (T1, T2) through which theflow subsequently passes, the first and the second subblock (T1 and T2)and also the third and the fourth subblock (T3 and T4) being arranged ineach case at the same height.
 10. A heat exchanger, in particularradiator for a heating or air-conditioning system of motor vehicles forthe cooling of coolant, which heat exchanger has air flowing through it,with header tubes (S1, S2, S3, S4) and with a plurality of tubes (5)arranged essentially in the horizontal direction, the heat exchanger (1)being subdivided into four subblocks (T1, T2, T3, T4) through which theflow passes in succession, characterized in that the temperature of thecoolant is higher in lower subblocks (T1, T2) than in upper subblocks(T3, T4), the temperature of one or of both rear subblocks (T1, T3)being higher than the temperature of the corresponding front subblock(T2, T4).
 11. A heat exchanger, in particular radiator for a heating orair-conditioning system of motor vehicles for the cooling of coolant,which heat exchanger has air flowing through it, with header tubes (S1,S2, S3, S4) and with a plurality of tubes (5) arranged essentially inthe horizontal direction, the heat exchanger (1) being subdivided intofour subblocks (T1, T2, T3, T4) through which the flow passes insuccession, characterized in that the temperature of the coolant ishigher in upper subblocks (T3, T4) than in lower subblocks (T1, T2), thetemperature of one or of both rear subblocks (T1, T3) being higher thanthe temperature of the corresponding front subblock (T2, T4).
 12. Theheat exchanger as claimed in claim 1, characterized in that the coolantis capable of flowing through at least two of the four subblocks (T1,T2, T3, T4) in cross countercurrent to the air.
 13. The heat exchangeras claimed in claim 1, characterized in that a diagonal deflection (6)is provided between two subblocks (T2, T3).
 14. The heat exchanger asclaimed in claim 13, characterized in that the diagonal deflection (6)takes place by means of a one-part transition flange (7) which isconnected to two header tubes (S2, S3).
 15. The heat exchanger asclaimed in claim 14, characterized in that the transition flange (7) haspartitions for the header tubes (S2, S3).
 16. The heat exchanger asclaimed in claim 15, characterized in that the transition flange (7) hastwo cylindrical recesses running parallel to one another and spacedapart from one another.
 17. The heat exchanger as claimed in claim 15,characterized in that the transition flange (7) has a passage whichforms a connection between the two header tubes (S2 and S3).
 18. Theheat exchanger as claimed in claim 13, characterized in that, in theregion of the diagonal deflection (6), at least one tube (5′) isprovided, through which coolant does not flow or flows only slightly.19. The heat exchanger as claimed in claim 1, characterized in that aconnection piece (9) which is connected to two header tubes (S1 and S2or S3 and S4) is provided at the inlet (2) and/or at the outlet (3). 20.The heat exchanger as claimed in claim 19, characterized in that theconnection piece (9) has a partition.
 21. The heat exchanger as claimedin claim 20, characterized in that the partition of the connection piece(9) is formed by the remaining portion of material of two cylindricalrecesses running parallel to one another.
 22. The heat exchanger asclaimed in claim 21, characterized in that the connection piece (9) hasa cylindrical recess which runs perpendicularly toward the partition andpartially penetrates the partition and which forms the supply ordischarge line.
 23. The heat exchanger as claimed in claim 1,characterized in that the flat tubes (5) are twisted in each casethrough 90° in the vicinity of the header tubes (S1, S2, S3, S4). 24.The heat exchanger as claimed in claim 23, characterized in that theflat tubes (5) are twisted through 90° upstream and downstream of a 180°bending point on that side of the heat exchanger (1) which is locatedopposite the header tubes (S1, S2, S3, S4).
 25. The heat exchanger asclaimed in claim 1, characterized in that the subregions (T1, T2, T3,T4) are closed off on both sides by means of header tubes (S1, S2, S3,S4).
 26. The heat exchanger as claimed in claim 25, characterized inthat at least two subregions (T1, T2, T3, T4) are closed off on at leastone side by means of a common header tube (S1, S2, S3, S4).
 27. The heatexchanger as claimed in claim 1, characterized in that the air flowingthrough the heat exchanger (1) comes into contact with two or moreregions of different temperature, the maximum air temperature differencebetween air inlet and air outlet being lower than one and a half timesthe temperature difference between coolant inlet and coolant outlet, thecoolant used being carbon dioxide in the supercritical state.
 28. Theheat exchanger as claimed in claim 1, characterized in that the tubes(5) arranged essentially in the horizontal direction are thermallyseparated from one another.
 29. The heat exchanger as claimed in claim1, characterized in that the individual subblocks are thermallyseparated from one another.
 30. The heat exchanger as claimed in claim1, characterized in that the header tubes are decoupled essentiallythermally.
 31. The heat exchanger as claimed in claim 1, characterizedin that cooling ribs are arranged between the tubes (5) arrangedessentially in the horizontal direction, the cooling ribs of theindividual subblocks, in particular of the subblocks which lie onebehind the other, being decoupled thermally.